A delusion is a symptome of schizophrenia or other disorders, mostly found in psychotic disorders. Being delusional means you have a strong false belief that is very unlike or even impossible to be real. But you are convinced and are not able to break this belief without help from the outside such as therapy and medication.
Schizophrenia is a psychotic disorders that has delusion as a symptome. Schizophrenia means you have lost the grip of reality, including negative symptomes (e.g. apathy, being tired all the time, no motivation etc) and positive symptomes (e.g. hallucinations, delusions, disorganized thinking).
(Please correct me if Im wrong)
I myself have psychosis and Im part of the schizophrenic/psychotic spectrum. I also have delusions, but Im treated with meds so Im aware of that which is not always the case. So I know a few things about these things so if you have more questions, feel free to ask!
Love&hugs, Ed